A framework to link localized cooling and properties of directed energy deposition (DED)-processed Ti-6Al-4V

Abstract

Additive manufacturing (AM) of titanium alloys is a rapidly growing field due to an increase in design flexibility of parts. However, AM parts are highly anisotropic in material microstructure and mechanical behavior due to the change of the local processing conditions in the build-up process. This study follows a link chain model to investigate the relationships between process parameters, cooling rate, porosity and mechanical behavior. The aim of this work is to present a framework that is inspired by the three-link chain model. The framework combines theoretical, computational and experimental approaches. We demonstrate this by using an in-house thermal simulator to link predicted cooling rates with micrographs describing experimental shape descriptors to develop a relationship between solidification cooling rate and porosity geometry. Finally, representative volume elements from predicted porosity maps allow for a prediction of mechanical properties at localized areas. The capability of being able to predict mechanical behavior of titanium alloys is demonstrated for the directed energy deposition process.

State of the Art in Directed Energy Deposition: From Additive Manufacturing to Materials Design

“…GED can be easily correlated with dilution. As shown in Figure 6c, lower values of GED lead to less dilution (the negative slope), meaning more propensity to a lack of fusion defect, whereas higher values of GED lead to high dilution (the positive slope), meaning more tendency to form keyhole porosity [85].…”

“…Intralayer porosity is linked to the use of inert shielding gas during the DED process, promoting gas entrapment. Intralayer pores are usually spherical in shape and occur at random locations, owing to vaporization leading to gas trapped porosities, and observed within regions having lower solidification cooling rates [82,85,86]. High dilution refers to the occurrence of intralayer porosities.…”

Modeling process-structure-property relationships for additive manufacturing

“…Macro-scale models for additive manufacturing are targeted at predicting the build process over several hours for a fully functional product spanning several centimeters in contrast to the millisecond/millimeter time scale of the previously aforementioned meso-scale models. The results of such models provide a prediction of temperature field and residual stress to evaluate the performance of the final product [19][20][21].…”

State of the Art and Emerging Trends in Additive Manufacturing: From Multi-Material processes to 3D printed Electronics

“…This occurs either by choosing parameters that lead to a certain porosity, or by producing structures that include voids in the input CAD file itself. By increasing porosity [35], material stiffness can be effectively lowered. These approaches are very similar in concept to the field of architectured materials and additively manufactured lattice structures.…”